Date: Mon, 26 Apr 2021 07:56:33 -0700 (PDT) From: "Rodney W. Grimes" <freebsd-rwg@gndrsh.dnsmgr.net> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: "Rodney W. Grimes" <freebsd-rwg@gndrsh.dnsmgr.net>, freebsd-hackers@freebsd.org Subject: Re: Are there any RFCs for address selection for IPv4 Message-ID: <202104261456.13QEuXEa098219@gndrsh.dnsmgr.net> In-Reply-To: <76578.1619447095@critter.freebsd.dk>
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> -------- > Rodney W. Grimes writes: > > > > Does anybody know why we put a (ipv6)LL on loopback interfaces ? > > > > I believe someplace in the bowls of all the IPv6 specs this > > is a requirement. I could not find it quickly though. > > I'm not seeing Linux doing it for instance ? I'll investigate further and see if I can discover why we do this, if it is or isnt in spec, etc. > > > Question: Should we allow a route to have a next hop of a LL(ipv4)? > > Reason: RFC3927 2.6.2: > > The host MUST NOT send a packet with an IPv4 Link-Local destination > > address to any router for forwarding. > > > > So, arguably, it is a violation to allow the default route to have > > a LL next hop for ipv4. For that matter, it is a violation to allow > > ANY ipv4 LL address to be the next hop in the routing table(s). > > You are reading that wrong. Yep > > It is OK to have a LL as next-hop. > > It is not OK to send a packet with dst=LL to any next-hop. No, that is explicity forbidden: RFC 3927 at 2.7 paragraph 2: An IPv4 packet whose source and/or destination address is in the 169.254/16 prefix MUST NOT be sent to any router for forwarding, and any network device receiving such a packet MUST NOT forward it, regardless of the TTL in the IPv4 header. If dst=LL you must ARP for the destination is also in the spec some place, no routing allowed. Now if you had said dst != LL to any next-hop, that would be true. > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > phk@FreeBSD.ORG | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org" > -- Rod Grimes rgrimes@freebsd.org
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